Radioisotope power system for vehicle

This application is a U.S. National Phase Application of International Application No. PCT/US2023/013846, filed on Feb. 24, 2023, titled “Radioisotope Power System for Vehicle” the entirety of which is incorporated by reference herein. International Application No. PCT/US2023/013846 claims priority to U.S. Provisional Patent Application No. 63/313,471, filed on Feb. 24, 2022, titled “Extrasolar Object Interceptor and Sample Return Enabled by Compact, Ultra Power Dense Radioisotope Batteries,” the entire disclosure of which is incorporated by reference herein.

This application relates to International Application No. PCT/US2023/013832, filed on Feb. 24, 2023, titled “Radiation Shielding for Radioisotope Battery-Powered Vehicle,” the entirety of which is incorporated by reference herein.

The present subject matter relates to examples of a radioisotope power system that includes a radioisotope battery for power, propulsion, or both power and propulsion of a vehicle. The present subject matter also encompasses a propulsion system that utilizes electric propulsion thrusters to propel the vehicle, such as a spacecraft or aircraft, which includes the radioisotope power system.

Conventional spacecraft systems utilize a chemical-reaction monopropellant rockets to propel an attached spacecraft through space. However, the chemical-reaction monopropellant acts both as the propulsive reaction and creates the resultant thrust. The propellant interacts with a catalyst, the propellant ignites, and the ignition of the propellant propels the ignited propellant out of a thruster in an opposite direction of intended travel of the spacecraft, generating thrust. Therefore, the propellant is typically selected to contain high levels of potential energy, be ignited by a relatively low-energy-cost reaction, and be relatively massive to maximize propulsion.

Some spacecraft systems incorporate a nuclear reactor system to implement a nuclear thermal propulsion (NTP) system. Such an NTP system utilizes the heat generated by a nuclear reactor to expand a propellant such as hydrogen through a nozzle to create thrust. The nuclear reactor provides thermal energy, and the propellant can be inert and maximize propulsive capability, with no concern for the energy-releasing properties of the propellant. NTP systems can achieve higher specific impulse (effective thrust per unit of propellant) than chemical-reaction propulsion systems and can perform about twice as efficiently. However. NTP systems are not well-suited for performing incredibly fast maneuvers, for example interception of an extrasolar object, which would require a propulsion system with a specific impulse ten or more times more efficient than chemical-reaction propulsion systems.

Size and mass are very important factors that impact the performance and efficiency of a vehicle, such as a spacecraft traveling to outer space, or an aircraft. For example, if the vehicle implements an NTP system and carries a nuclear reactor system (e.g., a fission nuclear reactor) for propulsion of the vehicle or to provide nuclear power (e.g., thermal and/or electrical power) in outer space, the size and mass are very important considerations. The mass of the nuclear reactor system being carried by the vehicle will directly affect performance, such as power per mass, in both the nuclear propulsion and power applications. The size of the nuclear reactor system may also add drag on the vehicle and increase manufacturing cost.

High-power density radioisotope batteries can be an ideal candidate to provide the energy required for the vehicle, such as a spacecraft, aircraft, etc. However, radioisotope batteries have challenges associated with their use. In particular, the x-rays and gamma rays emitted by certain radioisotopes can damage computer systems as well as harm humans. Additionally, radioisotope batteries still add significant size and mass to the vehicle even albeit somewhat less than the nuclear reactor system would.

Hence, there is room for further improvement in radioisotope power systems and vehicles that implement radioisotope power systems.

The radioisotope power systemand propulsion systemtechnologies disclosed herein increase the energy efficiency, mass efficiency, and duration capability of a vehicleduring operation, such as in outer space. Advantageously, the radioisotope power systemtechnologies can enable a vehicleto move faster for longer. To implement the radioisotope power system technologies, a spacecraftcan include a thermoelectric generatorto convert radiated heat from a radioisotope batteryinto electricity, and then can power a thruster, such as a field-emission electric propulsion (FEEP) thrusterA-N to accelerate a liquid metal propellant fast enough and long enough to, for example, catch an extrasolar object being launched by the sun's gravitational force.

The radioisotope power systemand propulsion systemdisclosed herein can increase the specific impulse or thrust-to-mass efficiency of the vehicle. Additionally, the radioisotope power systemand propulsion systemcan lengthen the total time the vehicleis able to sustain thrust, and the total amount of thrust. For example, the radioisotope power systemand propulsion systemare able to generate as much as approximately 150 km/s of thrust and sustain that thrust for over a decade.

In a first example, a radioisotope power systemincludes a radioisotope power unit. The radioisotope power unitemits a plurality of radiation particlesA-B and is configured to directly or indirectly provide power, propulsion, or both power and propulsion of a vehicle. The radioisotope power systemfurther includes a radiation shield. The radiation shieldis configured to block a first radiation particleA of the plurality of radiation particlesA-B. The radioisotope power unitcan include one or more radioisotopes. The one or more radioisotopes can include an alpha emitting isotope, a beta emitting isotope, a gamma emitting isotope, or a combination thereof. The radioisotope power unitcan be configured to provide propulsion to the vehicleby heating a propellant.

In a second example, a vehicleincludes a radioisotope power systemthat includes a radioisotope power unit. The radioisotope power unitemits a plurality of radiation particlesA-B and is configured to directly or indirectly provide power, propulsion, or both power and propulsion of a vehicle. The vehiclefurther includes at least one thrusterA coupled to the radioisotope power unit.

In a third example, a radioisotope power systemincludes a radioisotope power unit. The radioisotope power unitemits a plurality of radiation particlesA-B and is configured to directly or indirectly provide power, propulsion, or both power and propulsion of a vehicle. The radioisotope power systemfurther includes a thermoelectric generatorcoupled to the radioisotope power unitand configured for coupling to at least one thrusterA.

Additional objects, advantages and novel features of the examples will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and the accompanying drawings or may be learned by production or operation of the examples. The objects and advantages of the present subject matter may be realized and attained by means of the methodologies, instrumentalities and combinations particularly pointed out in the appended claims.

In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant teachings. However, it should be apparent to those skilled in the art that the present teachings may be practiced without such details. In other instances, well known methods, procedures, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present teachings.

The term “coupled” as used herein refers to any logical or physical connection. Unless described otherwise, coupled elements or devices are not necessarily directly connected to one another and may be separated by intermediate components, elements, etc.

Unless otherwise stated, any and all measurements, values, ratings, positions, magnitudes, sizes, angles, and other specifications that are set forth in this specification, including in the claims that follow, are approximate, not exact. Such amounts are intended to have a reasonable range that is consistent with the functions to which they relate and with what is customary in the art to which they pertain. For example, unless expressly stated otherwise, a parameter value or the like may vary by as much as +5% or as much as +10% from the stated amount. The terms “approximately,” “significantly.” or “substantially” means that the parameter value or the like varies up to +25% from the stated amount.

The orientations of the radioisotope power system, vehicle(e.g., spacecraftor aircraft), propellant tanksA-J, radiator finsA-E, propulsion system, associated components, and/or any complete devices incorporating the radioisotope power systemor vehicle, such as shown in any of the drawings, are given by way of example only, for illustration and discussion purposes. In operation, the radioisotope power systemand the vehiclemay be oriented in any other direction suitable to the particular application, for example upright, sideways, or any other orientation. Also, to the extent used herein, any directional term, such as lateral, longitudinal, up, down, upper, lower, top, bottom, front, rear, side, left, and right are used by way of example only, and are not limiting as to direction or orientation of any radioisotope power systemor vehicleor component of the radioisotope power systemor the vehicleconstructed as otherwise described herein.

The various examples disclosed herein relate to a radioisotope power systemand a vehicle, such as a spacecraftor aircraft, that includes the radioisotope power system. By utilizing the radioisotope power unit, the vehiclecan achieve significant mass savings compared to a conventional spacecraft that uses chemical batteries and fossil fuels for propulsion, for example. The vehiclecan include a propulsion systemthat includes field-emission electric propulsion (FEEP) thrustersA-N, which allows for implementation of liquid metal propellant. The liquid metal propellant improves volumetrics of the vehicleas well as removes pressurization requirements for propellant tanksA-E. Conventional fuels and propellants are too slow, too heavy, and too quick to burn up.

Additionally, the examples disclosed herein relate to radiation shielding of the radioisotope power systemand the vehiclevia a radiation shield (e.g., ejectable shield)and shadow shield. The radiation shieldcan be designed to protect people (e.g., ground personnel), but once the spacecraftpowered by the radioisotope batteryis in space, the radiation shieldis decoupled (e.g, ejected) from the spacecraft. Decoupling of the radiation shieldfrom the spacecraftcan result in a mass reduction of approximately 75%. In one example, utilizing the technologies described herein can enable a spacecraftto catch up to and capture extrasolar objects being slingshot by the sun.

Reference now is made in detail to the examples illustrated in the accompanying drawings and discussed below.

is front-perspective view of a vehicle(e.g., spacecraft) that includes a radioisotope power system, a plurality of propellant tanksA-E, a plurality of radiator finsA-E. and other components.is a back-perspective view of the spacecraftthat depicts the radioisotope power system, the plurality of propellant tanksA-E, the plurality of radiator finsA-E, and other components.is a side-perspective view of the spacecraftthat depicts the radioisotope power system, the plurality of propellant tanksA-E, the plurality of radiator fins-E. and other components.

Vehiclecan be a spacecraft, an aircraft, or a combination thereof. In the example of, the vehicleis a spacecraft(e.g., an extrasolar object interceptor). However, the vehiclecan be an aircraft. The vehiclemay function both as a spacecraftand an aircraft, for example, depending upon the presence or absence of an atmosphere. Vehiclecan also include electronics(see) configured to control the vehicle, an optional aeroshell, as well as a payloadand propulsion system. In example of, the vehicleincludes five propellant tanksA-E and five radiator finsA-E.

Radioisotope power systemincludes a radioisotope power unit(see) that emits a plurality of radiation particlesA-B to generate heat. The radioisotope power systemfurther includes a radiation shield(see) configured to block a first radiation particleA of the plurality of radiation particlesA-B (see). The radioisotope power systemfurther includes a decoupling deviceconfigured to decouple the radiation shieldfrom the vehicle(e.g., spacecraft). The decoupling devicemay be further configured to decouple the aeroshell. The radioisotope power unitcan include one or more radioisotopes for power, propulsion, or both power and propulsion of the vehicle. The radioisotope power unitcan be configured to provide propulsion to the vehicleby heating a propellant.

The one or more radioisotopes can include an alpha emitting isotope, a beta emitting isotope, a gamma emitting isotope, or a combination thereof. The one or more radioisotopes can be for beat generation. The radioisotope power systemcan further include a thermal interface(e.g., heat pipe), a radioisotope heater unit, a radioisotope electricity generator, a radioisotope power generator, a radioisotope thermoelectric generator (e.g., thermoelectric generator), or a combination thereof (see).

Radioisotope power unitcan be a radioisotope battery(see). The radioisotope battery(see) can be a nuclear battery, chargeable atomic battery (CAB), traditional atomic battery, etc., and can be formed of radioisotopes to generate heat, such as a nuclear chargeable ceramic. Radioisotope batterycan include, for example, Cobalt, Europium, Neptunium, Plutonium, or Thulium. A description of a radioisotope battery, such as a CAB, is provided in the following publications of Ultra Safe Nuclear Corporation of Seattle, Washington: U.S. Patent Pub. No. 2023/0023052, published Jan. 26, 2023, titled “Fully Ceramic Encapsulated Radioactive Heat Source”; U.S. Patent Pub. No. 2023/0051201, published Feb. 16, 2023, titled “Chargeable Atomic Battery and Activation Charging Production Methods”; and International Patent Pub. No. WO 2021/159041, published Aug. 12, 2021, titled “Chargeable Atomic Battery with Pre-Activation Encapsulation Manufacturing.”

In this example, the radioisotope power systemincludes a radioisotope power unitthat can include a radioisotope battery(e.g., Cobalt-60 thermal power source). However, the radioisotope batterycan include a variety of other radioisotopes besides Cobalt-60, such as Plutonium-238 (and fission products), Europium-152, Thulium-170, etc. Radioisotope power systemfurther includes a thermal interface(e.g., heat pipe) and a high-efficiency thermoelectric generator(see) to supply power to an electric propulsion system. Radioisotope batteryemits a plurality of radiation particlesA-B (see) as a consequence of the radioactive decay of the radioisotopes. The radioactive decay produces decay heat, which releases heat as the energy of the radiation is converted into thermal movement of atoms.

The example spacecraftofcan leverage the high specific impulse of electric propulsion without dependence on the sun, as would a purely-solar powered extrasolar object interceptor. The overall power balance from the radioisotope power unitis radiated as thermal power and converted to electrical power by a thermoelectric generator(), such as solid-state converters, and finally distributed to all electronicsof the spacecraft. Thus, the radioisotope power unitcan be configured to directly or indirectly provide energy to the electronics. In particular, voltages from solid-state converters are routed to a power management and distribution (PMAD) device which steps up the DC voltage for the field-emission electric propulsion (FEEP) thrustersA-N (see) of an electric propulsion system. Spacecraftcan also include solar sails in concert with the radioisotope battery(see) to enhance performance.

Radiation shieldcan comprise depleted uranium, natural uranium, lead, tungsten alloy, or a combination thereof. The radiation shieldcan also include a non-trace quantity of an element identified in a periodic table as a sixth period or greater element-meaning, elements with an atomic number, or number of protons, greater than or equal to fifty-five. If the radioisotopes in the radioisotope batteryinclude Thulium-170, then the radiation shieldcan primarily block x-ray emissions (the x-rays are generated by beta particles slowing down.) If the radioisotopes in the radioisotope batteryinclude Plutonium-238 (and fission products), Cobalt-60, Europium-152, etc., then the radiation shieldcan primarily block gamma radiation (high-energy photons emitted by a nucleus).

The radiation shieldis designed to protect humans (e.g., ground personnel) from the radiation particlesA-B (see) after integration of the vehiclewith the radioisotope power unit. In the spacecraftexample, integration can be before the interstellar portion of a mission. The radiation shieldcan be made from depleted Uranium. and can be designed to permit, at most, a 5 rem/hour of dose at 30 cm to ground personnel(see). The thickness or density of the radiation shieldcan be adjusted to ensure the radiation dose rate is below the U.S. Nuclear Regulatory Commission (NRC) definition of a radiation area and to be similar to the dose on the International Space Station (ISS. The radiation shieldrenders the radioisotope power unitsafe for ground crews of ground personnelto operate in proximity to the spacecraftfor extended periods of time (e.g, tens of hours).

Two components of the radioisotope power systemobviate the mass of radiation shieldand the need for the radiation shieldonce the spacecraftis in outer space(see): (1) the decoupling device; and (2) the shadow shield. Decoupling deviceis configured to remove the mass of the radiation shieldfrom a remainder of the spacecraft(seeandA-B). The remainder of the spacecraftis the spacecraftminus the radiation shieldand any portion of the decoupling devicenot remaining with the spacecraft(see). The decoupling devicecan include pyrotechnic or mechanical fasteners or actuators, or frangible nut and tension stud devices to eject the radiation shieldfrom the spacecraft. The decoupling devicemay split the radiation shieldinto two or more sub-shieldsA-B (see), in order to more efficiently propel the sub-shieldsA-B clear, away from the remainder of the spacecraft. The decoupling devicemay also include heating elements to melt some or all of the radiation shield, in order to decouple the radiation shieldfrom the remainder of the spacecraft, so that the radiation shieldis no longer in a deployed state. The shadow shieldremains deployed with the spacecraftto provide shielding to the components, such as electronics, which are sensitive to radiation, in outer space(see).

Remainder of the spacecraftcan decouple from or eject the radiation shield, or the radiation shieldcan decouple from or eject the remainder of the spacecraft. In a low-friction, floating environment such as space, after an ejection or decoupling, both the radiation shieldand the remainder of the spacecraftcan immediately proceed on opposite velocity vectors. Those opposite velocity vectors can be inversely proportional to the size of the radiation shieldand the remainder of the spacecraft, respectively. The radiation shieldis ejected from the remainder of the spacecraft, but the remainder of the spacecraftis also ejected from the radiation shield. Both trajectories are accounted for in planning a mission and determining whether the remainder of the spacecraftis clear from the radiation shield. Under another definition, an “ejector” may be the component (either the radiation shieldor remainder of spacecraft) which retains a larger proportion of the decoupling device. For example, when the decoupling deviceincludes a frangible nut, the component which retains the bolt may be considered the “ejector” component, while the component secured to the bolt by the frangible nut may be considered the “ejectee” component. Regardless, the decoupling devicecan have a larger proportion remain with the radiation shieldor a larger portion remain with the remainder of the spacecraftafter decoupling. The language of decoupling or ejecting should not imply a required directionality between the radiation shieldand the remainder of the spacecraft, based upon mass, acceleration, or remaining proportions of the decoupling deviceafter decoupling.

Payloadcan be any number of components or materials intended for use during the mission—in particular, including components or materials not directly related to facilitating space travel, such as those related to a sample collection subsystem(see). The payloadmay receive heat or electricity directly or indirectly from the radioisotope power unit. The payloadmay vary in size and mass over the duration of the mission, in particular, if the mission includes deploying or retrieving some object.

Propulsion systemcan be an electric propulsion system, which includes a type of ion thruster, such as FEEP thrustersA-N (see), that operate on the principle of field ionization of a liquid metal. For example, the propulsion systempumps a liquid metal propellant, such as indium, through an ionizing accelerator. The accelerator of the propulsion systemincludes an electrode capable of generating a strong electric field to accelerate and ionize the liquid metal propellant, creating a propulsive ion jet for thrust or power generation. Metal propellant can be electrically heated to change from a solid state to a liquid state. However, to improve the overall power efficiency of the electric propulsion system, the propellant can be heated using waste heat from the thermoelectric generator(see) before ionizing the propellant. Vehiclecan include any other type of conventional propulsion systemwhich can be powered by the radioisotope power unit, and any other type of conventional propellant which can be expelled or expanded to create thrust or motive force by the propulsion system.

is a cutaway view of a radioisotope power systemofdepicting details of the radioisotope power system, particularly a radioisotope power unit, radiation shieldand decoupling device, as well as other components of the spacecraft. Other depicted components include extendable boom(see also), aeroshell, and shadow shield.

In, decoupling deviceis depicted as embedded within the radiation shield. For example, the decoupling devicecan include a pyrotechnic designed to combust and split the radiation shieldinto two sub-shieldsA-B. As further radioisotope power systemincludes a safety impact liner, which can be an encapsulation layer around the entire radioisotope batterythat is resilient to impact, in particular during an accident, for example, during launch. Further, the safety impact lineris refractory, for example, heat resistant and difficult to melt.

Radioisotope power systemincludes a thermal interfacewhich can include a conductive interface, a heat pipe(e.g., lithium-based), or a combination thereof. Thermal interfacedirects heat produced by the radioisotope power unitto a thermoelectric generatorin order to provide heat to the thermoelectric generatorso that the thermoelectric generatorgenerates heat-based power (see). In the example, the thermal interfaceincludes a heat pipethat is coupled to the radioisotope batteryand circulates coolant, propellant, or a combination thereof, in order to heat the propellant for thrust.

Radioisotope power systemcan further include shadow shield, which is configured to block a second radiation particleB of the plurality of radiation particlesA-B (see). The decoupling deviceis configured to maintain coupling of the shadow shieldto the electronicsduring a mission (see), and does not disconnect, eject, or decouple the shadow shield. The electronicscan be configured to control the vehicle, including the propulsion system, the payload, the sample collection subsystem(see), the thermoelectric generator(see), the extendable boom, the decoupling device, the radioisotope power unit, other electrically, mechanically, or thermally-controlled components, or a combination thereof. The maintained coupling of the shadow shieldto the electronicsduring the mission can be configured to prevent some or all of the radiation particlesA-B from reaching the electronics. The radiation shieldcan be configured to block the first radiation particleA that travels around or is not blocked by the shadow shield. The shadow shieldcan be configured to block the second radiation particleB that is on a trajectory to intersect with electronics, payload, power modulation such as the thermoelectric generator(see), other sensitive components, or a combination thereof.

is a side view of the spacecraftofwith the radiation shieldcoupled to a balance of the spacecraft. The balance of spacecraftincludes all of the components of the spacecraftnot explicitly depicted in. Balance of spacecraftincludes, in part, the electronics, the payload, a sample collection subsystem(see), and the propulsion system, which may include FEEP thrustersA-N (see).

As shown in, in spaceflight deployments, the spacecraftcan include aeroshellto protect the spacecraftduring atmospheric exit. In some cases, the aeroshellcan further keep the radioisotope power unitfrom being released during an accident, e.g., as upon accidental atmospheric reentry during an event, such as a rocket launch failure. Such an aeroshellcan include the radiation shieldto protect any equipment or ground personnelfrom radiation emitted by the radioisotope battery. In other examples, the radiation shieldmay not be as purpose-built as an integrated radiation shielding aeroshell. Radiation shieldcan be formed as a cladding that encases the radioisotope power unit, particularly if the radioisotope batteryemits x-rays. In some cases, the aeroshellcan serve as additional radiation shielding to reduce the size of the main radiation shield.

is a cross-sectional view of the spacecraftlike that of, but depicting details of the radioisotope power unit, radiation shield, shadow shield, and thermoelectric generator. As shown in, the radioisotope power systemincludes the shadow shieldto provide mass effective spot shielding to components of the spacecraft. Shadow shieldcan be made of the same material as the radiation shield, or another shielding material. The shadow shieldmay be a sub-shield of the radiation shieldlike sub-shieldsA-B (see), but in such examples the shadow shieldremains in-place after the decoupling of the radiation shield. The shadow shieldis typically not decoupled or ejected from the spacecraftby the decoupling device. The shadow shieldis configured to protect the electronics. Consequently, the shadow shieldis smaller than the radiation shieldin both size and mass.

Balance of spacecraftincludes a sensitive volumethat can be protected from radiation flux of the radioisotope power unitby the shadow shield. The sensitive volumecontains the electronics, payload, and other sensitive equipment arranged therein. The electronics, payload, and other sensitive equipment in the sensitive volumemay be less sensitive to radiated particles than human personnel, and can require less shielding than the radiation shieldis required to provide.

As further shown in, the radioisotope power systemincludes a thermoelectric module housingand a thermoelectric generator. A description of a thermoelectric generatoris provided in the following publications of Ultra Safe Nuclear Corporation of Seattle, Washington: U.S. Patent Pub. No. 2023/0023052, published Jan. 26, 2023, titled “Fully Ceramic Encapsulated Radioactive Heat Source”; U.S. Patent Pub. No. 2023/0051201, published Feb. 16, 2023, titled “Chargeable Atomic Battery and Activation Charging Production Methods”; and International Patent Pub. No. WO 2021/159041, published Aug. 12, 2021, titled “Chargeable Atomic Battery with Pre-Activation Encapsulation Manufacturing.”

Thermoelectric generatorincludes thermoelectrics, such as an array of thermocouples, such as a thermopile, to convert the heat released by the decay of the radioisotope batteryin a radioactive state into electricity by the Seebeck effect. A thermopile is an electronic device that converts thermal energy into electrical energy and that includes several thermocouples as an array connected usually in series or, less commonly, in parallel. Thermoelectrics can include heavily doped semiconductors: semiconductors, which have so many free electrons that they have many properties that can generate electricity from the application of a temperature gradient, or vice versa, through the thermoelectric effect. For example, thermoelectrics can include solid-state devices that convert heat directly to electricity. The radioisotope power systemcan include a solid-state heat transfer component configured to move heat. Alternatively, the thermoelectric generatorcan include other conventional means of converting heat into electricity e.g., fluid turbines.

If the spacecraftincludes an extendable boom(see-B), then the thermoelectric module housingcan also be partially coupled to the extendable boom, which is further coupled to the balance of spacecraft. The thermoelectric generatorcan include thermoelectrics coupled to the radioisotope power unitto convert heat produced from radioactive decay of the radioisotope batteryinto electrical power (e.g., electricity production). Alternatively, the radioisotope power unitcan be used as an independent heat source for direct heat applications.

Generally, heat produced by the radiation particlesA-B (see) from the radioisotope batterycan be coupled to Stirling power converters, coolant/heating, or nuclear pulse propulsion systems. The heat can be utilized to provide thermal, electrical, or impulse energy for an external system requiring energy, such as satellites, lunar electronics, underwater vehicles, or remote heating devices. In the example of, the heat can be thermally coupled to the thermal interfaceand thermoelectric generator. Depending on the tolerance for radiation of these energy conversion means and any coupled electronic components, the thickness of any shadow shieldrequired may be greater. A conservative estimate for the tolerance of the electronicsis 25 kilorads (krad) in Silicon. Some electronicscan tolerate dose levels in the millirad (mrad) range. Techniques such as moving the electronics further from the radioisotope power unitmay help reduce the required mass of the shadow shield.

is an isometric view of the spacecraftlike that of, but depicting further details of the radiation shield, shadow shield, and radiator finsA-E. Radiator finsA-E may be connected to the propellant tanksA-E as shown in, such that radiator finA is connected to propellant tankA, radiator finB is connected to propellant tankB, etc. The radiator finsA-E may also be offset from the propellant tanksA-E at the same position along the length of the spacecraft, or may be offset from one or more propellant tanksA-E along the length of the spacecraft, as in. The radiator finsA-E may exhibit radial symmetry around the spacecraft, or the radiator finsA-E may be unevenly distributed.

Spacecraftincludes a launchcraft adapter plate, which can be used to attach the spacecraftto a launch vehicle capable of exiting Earth's atmosphere, referred to herein as a “launchcraft.” The example spacecraftmay not have the incredibly high sustained power required to substantially exit Earth's gravitational pull, but rather the example spacecraftinstead has the power to achieve high velocity in a zero-gravity environment. The launchcraft, such as a traditionally-designed, to-orbit, heavy-lift launch vehicle like the Vulcan Centaur or a Falcon, would latch onto the launchcraft adapter plate, launch itself with the spacecraftfrom Earth into orbit(see), and then release the spacecraftonce the spacecraftis brought to orbit.

is a cross-sectional view of the spacecraft like that of, but delineating the spacecraft, radiation shield, remainder of spacecraft, and balance of spacecraft. The spacecraftcan initially constitute the entire vehicle, generally as the spacecraftwould appear before commencement of a mission. The spacecraftis the summation of the radiation shield, the decoupling device, and the remainder of spacecraft.